Field of the Invention
Methods and systems for the decontamination of sulfur contaminates from vessels containing sulfur contaminants are provided. Specifically, methods and systems of using methylmorpholine-N-oxide to remove sulfur contaminants from vessels comprising water and/or gas contaminated with sulfur contaminants are provided.
Background of the Invention
Refineries and petrochemical plants are commonly contaminated with sulfur contaminants such as H2S. These sulfur contaminants may typically be mitigated or removed as part of decontamination procedures, for instance, prior to vessel (e.g., large storage tanks) entry by individuals. A conventional approach to decontamination is to use hydrogen sulfide scavengers (e.g., liquid scavengers) such as triazine, acrolein, or formaldehyde. Such scavengers may rely on non-oxidative complexation and may be an economical approach for H2S decontamination. Liquid scavengers may tie up H2S as water-soluble compounds that may be discharged to wastewater treatment facilities. However, such scavengers have drawbacks. For instance, some of the reaction products may not be water-soluble, and some of the treatment chemicals may have associated toxicity or environmental restrictions in certain locations. In addition, some sulfur contaminants may only be removed by specific scavengers, for example, typically only acrolein may neutralize pyrophoric iron sulfides. Additionally, triazine treatments may raise the pH of effluent streams and as a result, may promote the formation of scales on metal surfaces. Formaldehyde reactions with H2S typically produce water insoluble products. Further, acrolein benefits may be tempered by its toxicity.
Other methods have been developed and demonstrated to be effective at oxidizing and eliminating sulfur contaminants. Such methods include using permanganate (e.g., potassium permanganate), persulfate, sodium nitrite, ozone, hypochlorite, adducts of peroxide such as perborates and percarbonates, and long-chain amine oxides. The oxidizing chemicals may irreversibly convert sulfur contaminants (e.g., H2S) to harmless water soluble forms of sulfur, which may be compatible with effluent discharge. Each of these oxidizing compounds (i.e., oxidizing chemicals) have certain drawbacks. Hypochlorite may form dangerous chlorine compounds. Ozone and permanganate may involve field mixing. Permanganate decontaminations may be further complicated by large amounts of reaction solids that are typically processed at additional cost. Percarbonates, as with permanganate, may also be exothermic in their reaction, which may be particularly dangerous if hydrocarbon vapors are present. Further, treatments using strong oxidizers (i.e., permanganate, percarbonate, persulfate) are typically accomplished in small sequential batches outside the storage vessel in order to control the associated exotherm. As a result, these treatments may involve considerable time and therefore cost. The strong oxidizers may also be corrosive. Moreover, these compounds may also react violently with hydrocarbon components that may be present in sour sludge. For example, the strong oxidizers may be non-selective in their reaction and may react with many of the hydrocarbon components that may exist in sludge which may be contained in storage vessels. As a result, these treatments may be preformed in small sequential batches outside the vessel, which may increase operation time and expenditures.
Mild oxidizers such as amine oxides and nitrites may be effective at oxidizing sulfur contaminants to harmless forms of sulfur while having limited or having no effect on hydrocarbons, unlike strong oxidizers. Additionally, mild oxidizers may be added directly to a vessel as their associated reactions may be non-exothermic. However, mild oxidizers also have drawbacks. For instance, typical long-chain amine oxides may pose foaming issues due to their surfactant nature. These amine oxides may also have limited efficiency for large amounts of H2S, since they are typically diluted in water to prevent gel formation. Nitrites may also have drawbacks, as their reaction with hydrogen sulfide produces ammonia. As a result, the nitrite oxidation reaction may be accompanied by a rise in pH, which at some point may cease the oxidation before it is complete.
Consequently, there is a need for improved methods and systems for decontaminating vessels contaminated with sulfur contaminants.